In a wireless communications system, before receiving downlink data or sending uplink data, a terminal device needs to learn of scheduling information configured by a network device for the terminal device, for example, time-frequency resource allocation and a modulation and coding scheme. In addition, the network device also needs to inform the terminal device of power control command information related to uplink transmission. The scheduling information and the power control command information belong to downlink control information (DCI), that is, the DCI is for scheduling data transmission.
In an Long Term Evolution (LTE) system, a network device carries DCI mainly by using a physical downlink control channel (PDCCH). Currently defined PDCCHs, such as a PDCCH defined in the release Rel-8 and an enhanced PDCCH (EPDCCH) defined in Rel-11, are all used to schedule data transmission having a transmission time interval (TTI) length of 1 ms. However, to match different service requirements or scenario requirements, in the system, data transmission having a plurality of TTI lengths or data transmission having a plurality of scheduling priorities is required. In the prior art, a search space is usually located in the first one, two, three, or four symbols in a downlink subframe, or is located in a symbol area of a PDSCH. Therefore, a search space in an existing LTE system is configured only once in a subframe. For the data transmission having the plurality of TTI lengths or the data transmission having the plurality of scheduling priorities, flexibility of the search space is relatively poor.